The goal of this study is to develop a novel electrochemical S-nitrosothiol (RSNO) sensing system with an optimized detection limit and to finalize the specifications required to build a practical RSNO tool for clinical diagnostic applications. RSNO's are a primary carrier and reservoir of NO in vivo and are a potential pre-symptom marker for hypertensive disorders, endothelial dysfunction, cardiovascular risk and inflammation. However, the clinical significance of endogenous RSNO levels cannot be fully realized as a vascular diagnostic tool or biomarker without a quick and convenient assay for RSNO's. Compared to existing RSNO assay techniques, the proposed electrochemical RSNO sensor is highly sensitive and selective, is capable of rapidly measuring RSNO's in blood without separation or pretreatments and is suitable for simple and robust point-of-care use as a clinical diagnostic. A novel catalytic membrane will be prepared by covalently modifying cellulose dialysis membranes with selenocystamine to enhance the sensitivity of the RSNO sensor. The design parameters, including appropriate blood dilution ratios, light protection, temperature control, sensor/reagent stability and the tolerance to varying levels of blood components (e.g. hematocrit/hemoglobin) will be determined in Phase I and will serve as the criteria to build and validate the prototype point-of-care RSNO assay that will be assessed as a biomarker for pulmonary arterial hypertension (PAH) in Phase II. PUBLIC HEALTH RELEVANCE: The goal in this grant is to develop a novel electrochemical S-nitrosothiol (RSNO) sensor with enhanced limit of detection, and to determine the specifications to use this RSNO sensor as the detector to build a practical RSNO analyzer for clinical diagnostic applications, first for trial in pulmonary arterial hypertension (PAH). Currently there is no quick and convenient technique to measure endogenous RSNO concentrations reliably.